Method and system for setting application settings for a push-to-talk service

ABSTRACT

A Multimedia system and a method in a Multimedia system where a first user with user equipment ( 1 ) uses a Push to talk service (PTT) to communicate with at least one second subscriber&#39;s user equipment ( 2 ) using said Push to talk service (PTT), wherein a PTT-server ( 3 ) providing the PTT-service interacts with said first and second subscriber&#39;s user equipment ( 1, 2 ) and exchanges information concerning relevant parameter values for each user equipment ( 1, 2 ), and each user equipment ( 1, 2 ) adapting its application settings during the operation of said PTT-service, whereby degradation of the perceived quality is prevented

TECHNICAL FIELD

The present invention relates to a multimedia system where a first userequipment uses a Push to talk service (PTT) to communicate with at leasta second user equipment using said Push to talk service (PTT).

BACKGROUND

Many telecommunications operators want to have common infrastructure fornew service introduction. The so called IP Multimedia System (IMS) is atechnology standardized by 3GPP. It adds the ability to deliverintegrated voice and data services over the IP-based packet switchednetwork.

The IP Multimedia System (IMS) enables a 3G system being specified by3GPP to both benefit from the use of Internet Protocols (IPs) and offerscapabilities that IP is designed to provide. These include access toInternet and multimedia content. IP offers a number of attractions overtraditional telecommunications protocols: in addition to representing abridge between the telecommunications and Internet worlds, it alsooffers a “seamlessness” of communication over many different types ofnetworks. As a result, customers will experience extremely flexibletelecommunications, irrespective of the various networks over whichtheir calls may pass.

One type of service that can be even more valuable for operators andtheir customers is the Push-to-talk (PTT) service implemented in IMS.

Push-to-talk (PTT) is basically a “walkie-talkie” in a cellulartelecommunication system. Push-to-talk systems are typically used insettings where a group of geographically diverse people requirecommunications with each other in a “point-to-multipoint” fashion.Examples of push-to-talk system uses include workgroup communications,security communications, construction site communication, and localizedmilitary communications. The new service PTT providing groupcommunication services is applicable to both real-time data, such asaudio and video data (including voice data), and time-independent data,such as computer files, email, and so on.

Earlier known system is Land Mobile Radios, which have been used intrucks, taxis, buses, and other vehicles in order to communicatescheduling information between a central dispatch centre and one or morecorresponding fleet vehicles. Communications may be directed at aspecific vehicle in the fleet or to all vehicles simultaneously. Thesesolutions are based on different technology. Another known solutionbased on cellular technology is the solution that the US operator Nextelhas sold as a proprietary PTT-solution. This solution is called DirectConnect and is based on Motorola's iDEN (integrated Digital EnhancedNetwork) technology. A drawback with this solution is that theirversions of the special connection calls require that all members arelocated in the same area served by one BSC (Base Station Controller).Another drawback is that it is not based on any standard protocols, suchas RTP, and thus suffers from bandwidth problems.

WO 01/37526 discloses a general method and an apparatus for providingpush to talk functionality to a conventional wireless phone. Basically,the document discloses providing an input mechanism or button thatfunctions as a conventional telephone function while the telephone isused in conventional telephone mode, and that functions as a push totalk function while the telephone is in a push to talk mode. Thedocument does not disclose how the telephone interacts with either aPTT-server or another telephone.

EP 0 876 072 discloses a scalable radio platform for wirelesscommunication system which can interface with user equipment or systemequipment to allow system parameters to be modified such that users ofdifferent communication systems can communicate with each other, andalso allows a wireless communication system to adapt to changing radioconditions. However, the document does not disclose any pointers as tohow the quality of a PTT-session between two or more subscribers withuser equipment can be improved or prevented from degrading.

SUMMARY

A general object of the present invention is to provide an improvedPush-to talk service in a multimedia system.

A further object of the present invention is to provide a solution forpreventing degradation of the user-perceived quality for a Push to talk(PTT) service in a multimedia system.

Another object is to provide a solution for a more efficient utilizationof available bandwidth to a PTT-service in a multimedia system.

Yet, another object of the present invention is to set the appropriateapplication settings of the PTT-service with respect to the systemcharacteristics (such as the radio environment, and available mechanismin the PTT-system, e.g. header compression).

The invention is based on the recognition that during a Push to talksession involving at least two user equipment, and a Push to talk serverproviding the service, the quality of the radio link is typicallydifferent from one user equipment to another. As a consequence, when afirst user equipment initiates and transmits speech over one radio linkwith a specific quality and a second user equipment receives the speechover another radio link with its specific quality, unwanted delay can beintroduced. Also other undesirable effects may be introduced, includingloss of speech data packets, whereby the overall quality of the sessionis degraded.

In order to achieve the above mentioned objects, a general embodimentaccording to the invention is provided in a Multimedia system where afirst user equipment uses a Push to talk service (PTT) to communicatewith at least one second user equipment using said Push to talk service(PTT). Furthermore, a PTT-server interacts with the first and seconduser equipment, information for adaptation of user equipment applicationsettings is exchanged between the equipment and the PTT-server duringthe interaction, finally the application settings are adapted duringoperation of the PTT-service.

Another general embodiment of the invention comprises that at least oneof a first and a second user equipment report its PTT session parametervalues for PTT application settings in said user equipment to thePTT-server. New PTT session parameter values are determined based onsaid reported PTT session parameter values and at least one of saidfirst and second user equipment adapting its PTT application settingsduring session operation of said service.

According to a more specific embodiment of the invention, at least oneof the first and second user equipment determines their respectiverelevant parameter values for the application service and reports theseto the PTT-server. Based on the reported parameters the PTT-serversuggests or communicates suitable new parameter values or applicationsettings to the user equipment. Finally, the equipments adapt theirrespective parameter values according to the information from thePTT-server.

In a further embodiment, the PTT-server communicates the receivedparameter values to at least one of the first and second user equipment.The user equipment then generates new parameter values based on receivedvalues and possibly on its own old parameter values. An updating oradaptation of the PTT application settings is then performed in the userequipment using the generated parameter values.

According to a more specific exemplification of an embodiment accordingto the invention in a Multimedia system where a first user equipmentuses a Push to talk service (PTT) to communicate with at least onesecond subscriber's user equipment using said Push to talk service(PTT), where:

at least one of said first and second subscriber equipment signal thedetermined parameters values to said PTT-server and/or to other of saidfirst and second equipment which do not have said parameters values, and

said PTT-server collects the determined parameter values from said firstand second user equipment and provides information of suitableapplication settings for all of said first and second user equipment.

In addition, said signalling is performed using on or several of thefollowing methods: SIP/SDP, In-band channel, RTP, RTPC, specific radioprotocol.

According to a possible embodiment according to the invention, saidsecond user equipment are a plurality of user equipment and several ofsaid plurality of user equipment have high bandwidth links and one or afew of said second user equipment have poor radio environment and thesaid PTT-server can chose to:

-   -   a) order all of first and second subscriber equipment to use a        robust settings (all subscriber have the same settings as the        one with the lowest link quality);    -   b) perform adjustment to the transmitted data in said PTT-server        for the user which has the lowest quality; and/or    -   c) drop the user with the lowest quality.

The adaptation of the application settings can be performed according toreceived information according to the following:

-   -   a) number of frames in an IP-packet are adopted in-between two        talk spurts either when a special button on subscriber equipment        are released or during silence periods in the speech (detected        by a voice activity detection algorithm);    -   b) coder mode may be adopted during speech;    -   c) frame buffer depth are adopted in-between two talk spurts        either when a special button on subscriber equipment are        released or during silence periods in the speech (detected by a        voice activity detection algorithm); and/or    -   d) other relevant parameters will be adopted in periods where        they not disturb the system quality.

According to the invention a Multimedia system is provided where a firstuser equipment uses a Push to talk service (PTT), with specificapplication settings, to communicate with one or several secondsubscriber's equipment using said Push to talk service (PTT) and wheredegrading of the perceived quality is prevented. The PTT-serverinteracts with said first and second user equipment while saidapplication settings are changed during the operation of said service,and said first and second user equipment and PTT-server exchangeinformation for adaptation of said application settings.

Also, a PTT-server and a user equipment are provided according to theinvention.

Advantages of the present invention are:

-   -   An improved utilization of available bandwidth.    -   Prevention of degradation of perceived quality.    -   Reduction of delay during a session.

Other advantages offered by the invention will be appreciated uponreading of the below description of the embodiments of the invention.

The main advantage of the invention is that the invention makes itpossible to create a better infrastructure for operators whichsubscribers can benefit from and further creating a system with, inaverage, lower delay and higher perceived quality of service.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, maybest be understood by making reference to the following descriptiontaken together with the accompanying drawings, in which:

FIG. 1 is a schematic overview of a multimedia system;

FIG. 2 is a schematic flow diagram of an embodiment of a methodaccording to the invention;

FIG. 3 is a schematic flow diagram of another embodiment of a methodaccording to the invention;

FIG. 4 is a schematic block diagram of an embodiment of a PTT-serveraccording to the invention;

FIG. 5 is a schematic block diagram of an embodiment of a user equipmentaccording to the invention; and

FIG. 6 illustrates the optimal number of frames per IP-packet for GPRS 1time slot. An average IP/UDP/RTP header size of 3 bytes is assumed forthe header compression (HC) case.

DETAILED DESCRIPTION

A glossary of the abbreviations used in this detailed description of theinvention is set out below to facilitate an understanding of the presentinvention. CDMA Code Division Multiple Access RTCP Real Time ControlProtocol SIP Session Initiated Protocol SDP Session Description ProtocolBLER Block Error Rate AMR Adaptive Multi Rate IPv6 Internet Protocolversion 6 WCDMA Wideband Code Division Multiple Access GSM Global Systemfor Mobile communication EGPRS Enhanced GPRS GPRS General Packet RadioServices UDP User Datagram Protocol RTP Real Time Protocol IP InternetProtocol PTT Push-to-talk

For at better understanding of the invention, it may be useful to beginwith a brief system overview and analysis of the problem.

The system in which the invention is implemented is an IP MultimediaSubsystem (IMS) as specified by 3GPP for enabling IP connections betweenmobile phones.

Basically, a Push to talk service (PTT) between a first subscriber'suser equipment 1 and at least a second subscriber's user equipment 2 isprovided by a PTT-server 3, as is illustrated in FIG. 1.

The task of the PTT server 1 is to handle multimedia conferencingbetween two or more end-points in a packet switched network and mix thedata streams, which belongs to the same conference. Conferences orsessions are set up with the PTT server 3 as a centralised conferencebridge, mixing the different media streams and interact with userequipment 1, 2.

The PTT-service relies on a dedicated channel, over which communicationsare received by the wireless telephones. Only one member or userequipment 1, 2 may transmit information to the other members or userequipments at a time. However, all members can listen to the dedicatedbroadcast channel to receive communications from the single member whois transmitting. Subscribers desiring to transmit to other members ofthe system typically send an access request by depressing a push-to-talcbutton on a respective communication device, which allows sole access tothe dedicated transmission channel. The dedicated channel is sometimesreferred to as a broadcast channel.

There are typically two different types of PTT-sessions, so calledone-to-one and one-to-many, as indicated in FIG. 1.

For the case of a one-to-one session between two mobile telephonesubscribers, e.g., A and B. When A wishes to have communication with B,A enters B's private identification number, holds down a push to talk(“PTT”) button on the user equipment 1, waits for an audible alertsignifying that B is ready to receive, and starts speaking. To listen, Areleases the PTT button. If B wishes to speak, B holds down the PTTbutton on its user equipment 2 and waits for an audible confirmationthat A is ready to receive.

For the case of one-to-many, a pre-defined group of subscribers isidentified by a number. In order for a subscriber to place a group call,the initiating subscriber, e.g., A, locates a group number in the userequipment 1, holds down the PTT button, and, upon receiving an audibleconfirmation such as a peep, can start speaking. All of the other groupmembers on the group call can only listen while A is holding down thePTT button. If A releases the PTT button, another member on the groupcall may hold down the PTT button, acquire control signalled by theaudible confirmation, and start speaking.

PTT enabled phones will most likely be equipped with a hardware orsoftware PTT-button. When the PTT-button is pressed, the phone connectsyou directly to a friend, a family member or even a whole group ofpeople of your choice. Like a “walkie-talkie”, the PTT-service issimple. Thanks to the fast connection, e.g. not having to dial a number,the user can start to speak immediately after pressing the button. ThePTT-service handle 1-to-1 direct calls as well as 1-to-many calls (groupcalls).

PTT is a packet switched application, which means that the PTT servicesends the speech in IP/UDP/RTP-packets over a GPRS or EGPRS bearer inGSM-systems and over the interactive or the streaming radio bearer inthe WCDMA systems. One gain with the PTT-service compared to traditionalvoice services in cellular systems (compared to circuit switchedtechnologies) is that resources in the systems are only used whensomeone is talking even though the users have a virtual connection thatmay last a whole day (or more).

From a High Level Perspective, the Typical PTT Service Works Accordingto the Following:

When the PTT-button is pressed down, a fast session initialization isperformed. Basically, the transmitting user equipment 1 sends a SIPmessage to a PTT-server 3 in order to invite the other user(s) 2 to asession. When the PTT-server 3 has responded with an OK, the handset 1starts to transmit coded speech in IP/UDP/RTP-packets.

Depending on the radio environment for the users involved in thesession, the available bandwidth for the PTT-service will change in time(and space). Hence, the user-perceived quality might drop from anacceptable level to an unacceptable level due to large delays and/or ahigh rate of lost speech frames.

Therefore, to obtain as high quality of service as possible it isnecessary, according to the invention, that a number of applicationsettings can be changed during the operation of the service.

When the PTT-button is released, SIP messages signal that the session isover and every handset or user equipment in the session goes down toidle mode. Even though the handsets go down to idle, the handsets shouldbe able to change their application settings depending on either radioenvironment measurements/determination or reports that are sent to thehandset from the PTT-server.

The system characteristics have significant influence on availablebandwidth for the PTT-service. With appropriate application settings thebandwidth is efficiently used thus optimizing the perceived quality ofthe service.

A general embodiment of a method according to the invention comprisesthat a PTT-server 3 interacts with first 1 and second 2 user equipment,information for adaptation of application settings is exchanged betweenthe user equipment 1, 2 and the PTT-server 3 during the interaction, andfinally the application settings are adapted during operation of thePIT-service.

Referring to FIG. 2, another general embodiment of a method according tothe invention is illustrated. The method starts with an initiation of aPTT-session involving at least a first and a second user equipment instep S1. Thereafter at least one of a first and at least a second userequipment reports PTT session parameter values for PTT applicationsettings in said user equipment to the PTT server in step S2. A nextstep S3 determines new PTT session parameter values based on saidreported PTT session parameter values. Finally, at least one of saidfirst and second user equipment adapts its PTT application settingsduring the operation of said PTT service in step S4.

According to another more detailed embodiment of a method according tothe invention, the interaction between the PTT-server and the first andsecond user equipment comprises that during a PTT-session at least oneof said first and second user equipment determines relevant PTT-sessionparameters for its PTT application settings. The user equipment reportsthe determined parameter values to the PTT-server. The PTT-servercollects the reported parameter values and distributes the collectedparameter values either raw and/or as suggested application settings inan effective manner to the each user equipment. Finally, the userequipment adapts their application settings in response to thesuggestion from the PIT-server.

A detailed exemplary embodiment of a method according to the inventionis described below, with reference to FIG. 3.

Initially, in a first step S10, a PTT-conversation or session is set upor started by a first subscriber with user equipment according to knownprocedures i.e. the first subscriber pushes a PTT-button at a userequipment and awaits an acknowledgments signal. In this set up, typicalapplication settings such as number of frames per IP packet, coder mode,frame buffer depth etc. are utilized.

In a second step S11 during the PIT-session, said first and second userequipment, measures and/or determines the relevant PTT-session parametervalues for their PTT application settings according to at least one ofthe parameters in the following:

-   -   a) Received bit rate    -   b) Maximum possible bit rate    -   c) Coding scheme used    -   d) Number of time slots used    -   e) Header compression used or not    -   f) . . . other relevant PTT-session parameter values

In the above mentioned step both of said first and said second userequipment determines relevant parameter values. However, it isanticipated by the invention that only one of the first and second userequipment could perform this determining step. This user equipment isthen typically the receiving user equipment.

Subsequently, in a third step S12 of the embodiment of a methodaccording to the invention, said first and second user equipment signalor report their respective determined parameter values to the PTT-serverand possibly to the other user equipment as well. The PTT-servercollects all said determined parameter values and determines on suitableapplication settings for each user equipment.

It is however implied that the PTT-server might relay reported parametervalues from one user equipment to another.

In a fourth step S13, according to the embodiment, the PTT-serverprovides or signals information regarding the determined suitableapplication settings to the concerned user equipment. The signaling canbe performed by means of any one of SIP/SDP, In-band channel, RTP, RTCPor some specific radio protocol.

The information may comprise raw parameter values or suggestedapplication settings, thereby leaving the adaptation decision to theuser equipment.

However, in some other application or embodiment, preferably each userequipment determines its own suitable application settings, based oncommunicated information about other user equipment from the PTT-server.

For the case of multiple second user equipment it is possible to have aplurality of said multiple second user equipment with high bandwidthlinks and at least one second user equipment with poor radioenvironment. The PTT-server can choose to selectively inform the userequipment on how to adapt the application settings.

A first possible adaptation is to force all user equipment to use arobust application setting, whereby all user equipment have to adapt tothe application settings of the user equipment with poorest radioenvironment.

Another possible adaptation is to only inform the user equipment withthe poorest quality of any changes to application settings.

Finally, but not preferably, dropping the user equipment with thepoorest radio environment.

Finally, in a fifth step S14, said first and second subscriber's userequipment adapts their respective application settings according to theinformation provided by the PTT-server. The various applicationparameters can be adapted either in-between two talk spurts or duringspeech. Examples of the different cases can be performed according tothe following, it is however implied that most of the applicationsettings can be adapted during speech.

The number of frames in an IP packet may be adapted in-between two talkspurts, either when the PTT-button is released or during silence periodsin the speech, as detected by a Voice Activity Detection algorithm.

Coder mode may be adapted during speech.

Frame buffer depth may be adapted in-between two talk-spurts, similarlyto the number of frames.

Other relevant application settings can be adapted in a similar manner,either during speech or in-between two talk spurts.

A general embodiment of a multimedia system according to the inventioncomprises means for reporting PTT-session parameter values from at leastone of first and second user equipment to a PTT-server, means fordetermining new parameter values for at least one of said userequipment, and means for adapting the application settings of said atleast one of said first and second user equipment based on said newparameter values.

FIG. 4 illustrates a schematic block diagram of an embodiment of aPTT-server 3 according to the invention. The PTT-server 3 comprisesfirst means 31 for receiving reported PTT-session parameter values fromsaid first and second user equipment, and second means 32 fordetermining or optimizing new PTT parameter values for at least one ofsaid first and second user equipment. Said first means 31 typicallycomprises an I/O unit 31 for communicating with said first and seconduser equipment, thereby providing reporting functionality for reportingdetermined new PTT parameter values.

The second means 32 are optional, since it is possible according toanother embodiment, to perform the determination of new PTT-sessionparameter values at a user equipment. For that case the second means 32acts as a relay unit, forwarding received reported parameter values forat least one of said first and second user equipment to at least oneother of said first and second user equipment.

FIG. 5 illustrates a schematic block diagram of an embodiment of a userequipment 1 according to the invention. The user equipment 1 comprisesan I/O-unit 11 for communicating with the PTT-server and other userequipment, first means 12 for determining PTT session parameter valuesfor PTT application settings, second means 13 for adapting PTT sessionparameter values and third optional means 14 for determining oroptimizing new parameter values or application settings.

The I/O unit 11 provides functionality for reporting determined PTTparameter values to the PTT-server and to receive communicated newparameter values and/or suggested application settings from thePTT-server and/or other user equipment. The adaptation unit 13 adaptsthe PTT-session parameter values based on the new parameter valuesreported by the PTT-server and/or

An exemplification of a case of adaptation of application settings willbe described below, with reference to FIG. 6.

A GPRS bearer suffering from a “bad” radio environment would mean thatcoding scheme CS1 is used. If we assume a Block Error Rate (BLER) of 10%the available bandwidth of such system becomes: ˜7.2 kbit/s.

Further, it is assumed that the AMR speech coder operates at the 5.15kbit/s coder rate. We also assume that the speech frames are packed inIPv6/UDP/RTP packets and that the AMR payload format is used. In thecase of no header compression, 16 speech frames (see FIG. 6) must bepacked in one IP-packet, hence creating a packetizing delay of 320 ms.In the case of a good radio environment, coding scheme CS2 might beused. Even with the same BLER (10%) the number of frames in an IP-packetcan be reduced to 6 frames, this would give a packetizing delay of 120ms.

Therefore, if adjustment of this application setting is possible thenthe packetizing delay can be reduced with 200 ms. Further, thetransmission delay at every radio link is also reduced when eachIP-packet becomes smaller and thus needs shorter transmission time.

To be able to set an appropriate value of the number of frames perIP-packet a set of relevant parameters must be determined. In theexample above, we could have determined the bandwidth of the PTT-channelor the coding scheme that was used and the number of time slots used.Another parameter that is possible to “measure” or determine is ifheader compression is used. (Further reductions of the number of framespacketized in one IP-packet can be done if header compression is used,see FIG. 6).

The present invention is described in the context of a push to talkservice in a multimedia system. However, the same general idea isapplicable to any other push-service where information is supplied inthe form of IP packets, e.g. text, video, photos etc.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1-19. (canceled)
 20. A method in a multimedia system where a first userwith user equipment (1) uses a Push to talk service (PTT), provided by aPTT-server (3), to communicate with at least a second user equipment (2)using said Push to talk service (PTT), said method comprising the stepsof: at least one of said first (1) and second (2) user equipmentreporting at least one PTT session parameter value for its PTTapplication settings to the PTT server (3); determining new PTT sessionparameter values for at least one of said first (1) and second (2) userequipment based on said reported at least one PTT session parametervalue; and, at least one of said first (1) and second (2) user equipmentadapting its PTT application settings during operation of said servicebased on said new PTT session parameter values.
 21. The method recitedin claim 20, wherein each said first (1) and second (2) user equipmentreports its at least one PTT session parameter value to the PTT-server(3).
 22. The method recited in claim 20, wherein said determining stepcomprises the steps of: said PTT-server (3) forwarding said reportedparameter values of said first (1) and second (2) user equipment to atleast one of said first (1) and second (2) user equipment that does nothave said parameter values; and, said at least one of said first (1) andsecond (2) user equipment determining new parameter values based on saidreported parameter values and its own parameter values.
 23. The methodrecited in claim 20, wherein said determining step comprises the stepsof: said PTT-server (3) determining new parameter values for at leastone of said first (1) and second (2) user equipment based on saidreported parameter values from at least one of said first (1) and second(2) user equipment; and, said PTT-server (3) forwarding said newparameter values or suggested application settings based on said newparameter values to said at least one of said first (1) and second (2)user equipment.
 24. The method recited in claim 20, wherein saidapplication settings at the beginning of the conversation compriserelevant parameter values such as number of frames per IP-packet, codermode, frame buffer depth and other specific application settings. 25.The method recited in claim 20, wherein said first (1) and second (2)user equipment determine and report one or several PTT session parametervalues such as received bit rate, maximum possible bit rate, codingscheme used, number of time slots used, header compression used or not,and other specific applications settings.
 26. The method recited inclaim 20, wherein at least one of said first (1) and second (2) userequipment reports the determined parameter values to said PTT-server (3)and/or to other of said first (1) and second (2) user equipment which donot have said parameter values.
 27. The method recited in claim 20,wherein said PTT-server (3) collects the determined parameter valuesfrom all of said first (1) and second (2) user equipment and providesinformation of suitable application settings to all of said first (1)and second (2) subscribers equipment.
 28. The method recited in claim20, wherein said reporting step is performed using at least one ofSIP/SDP, In-band channel, RTP, RTCP, specific radio protocol.
 29. Themethod recited in claim 20, wherein said first user equipmentcommunicates with multiple second user equipment (2).
 30. The methodaccording to claim 29, wherein when a majority of said multiple seconduser equipment (2) have high bandwidth links and at least one of saidmultiple second user equipment (2) has poor radio environment, saidPTT-server (3) chooses one of: ordering all said first (1) and second(2) user equipment to use a robust settings, whereby all user equipment(1, 2) have the same application settings as the at least one with thelowest link quality; or performing adjustment to the transmitted data insaid PTT-server (3) for the user equipment with the lowest link quality,or dropping the user equipment with the lowest link quality.
 31. Themethod recited in claim 20, further comprising the step of adapting theapplication settings in-between two talk spurts according to either:when a special button on a user equipment (1, 2) is released or duringsilence periods in the speech as detected by a voice activity detectionalgorithm; and/or during speech.
 32. The method according to claim 31,further comprising the step of adapting the application settingsaccording to at least one of: number of frames per IP-packet in-betweentwo talk spurts; coder mode during speech; frame buffer depth in-betweentwo talk spurts; and, other relevant parameters in periods where they donot disturb the system quality.
 33. The method according to claim 20,further comprising the step of adapting said application settingsdynamically.
 34. A multimedia system wherein a first user with userequipment (1) uses a Push to talk service (PTT), provided by aPTT-server (3), to communicate with at least a second user equipment (2)using said Push to talk service (PTT), said system comprising: means(11) for reporting its PTT session parameter values for at least one ofsaid first (1) and second (2) user equipment PTT application settings tothe PTT server (3); means (14, 32) for determining new PTT sessionparameter values for at least one of said first (1) and second (2) userequipment based on said reported PTT session parameter values; and,means (13) for adapting the PTT application settings for at least one ofsaid first (1) and second (2) user equipment during operation of saidservice based on said new PTT session parameter values.
 35. A push totalk server (3) in a multimedia system wherein a first user with userequipment (1) uses a Push to talk service (PTT), provided by thePTT-server, to communicate with at least a second user equipment (2)using said Push to talk service (PTT), said system comprising: means(31) for receiving PTT session parameter values from at least one ofsaid first (1) and second (2) user equipment for their respective PTTapplication settings; means (32) for determining new PTT sessionparameter values for at least one of said first (1) and second (2) userequipment based on said reported PTT session parameter values; and,means (31) for communicating said new PTT parameter values or suggestedPTT application settings to at least one of said first (1) and second(2) user equipment.
 36. The push to talk server according to claim 35,wherein said communicating means (31) are adapted to relay reported PTTsession parameter values from said at least one of said first (1) andsecond (2) user equipment to other of said first (1) and second (2) userequipment.
 37. A user equipment (1) adapted for communicating with atleast a second user equipment (2) in a multimedia system using a Push totalk service (PTT), provided by a PTT-server (3), said user equipmentcomprising: means (11) for determining PTT session parameter values forPTT application settings; means (12) for receiving PTT session parametervalues from the PTT-server (3); means (14) for determining newPTT-session parameter values based on said received and said determinedPTT-session parameter values; and, means (13) for adapting the PTTapplication settings based on the determined new parameter values.
 38. Auser equipment (1) adapted for communicating with at least a second userequipment (2) in a multimedia system using a Push to talk service (PTT),provided by a PTT-server (3), said user equipment comprising: means (11)for determining PTT session parameter values for PTT applicationsettings; means (12) for reporting PTT session parameter values to thePTT-server (3) and for receiving new PTT session parameter values and/orsuggested application settings from the PTT-server; and, means (13) foradapting the PTT application settings based on the determined newparameter values.